NE5565 electronic ballast controller

Abstract: NE5565 is an electronic ballast controller launched by Philips that integrates PFC and half-bridge driver. This article introduces its internal structure, main features and functions, and gives a typical application circuit. Keywords: ballast control IC; PFC; half-bridge drive; three-step soft start; NE5565 NE5565 is an electronic ballast controller launched by Philips. This bipolar monolithic IC integrates a power factor correction (PFC) controller and a self-oscillating half-bridge driver with various control and protection functions. Using NE5565 to design electronic ballasts for fluorescent lamps can reduce the number of components, reduce volume, reduce weight, and improve the reliability and safety of the ballast. 1. Internal structure and main features of NE5565 　　EN5565 adopts a 20-pin dual in-line narrow-body plastic package, as shown in Figure 1. NE5565 mainly consists of power factor (PF) amplifier, DC error amplifier, PWM controller, half-bridge oscillator, output buffer, voltage regulator, lamp voltage regulator, lamp current rectifier and under-voltage lockout protection, capacitive load protection, Overcurrent protection and other circuit components are shown in Figure 2. The NE5565 pin functions and pin input and output ratings are listed in Table 1. 　　The NE5565 controller includes two switching power supply control circuits: the first is a PFC boost converter controller, which can increase the electronic ballast power factor to more than 0.99 with extremely low current harmonic distortion while being very responsive to AC transient voltages. Provide protection; the second is a half-bridge oscillator circuit, which converts the DC high voltage output by the PFC into a high-frequency AC voltage. The half-bridge controller drives two external high-voltage power MOSFETs to achieve functions such as lamp current regulation, peak lamp voltage limitation, and power switch protection. The operating temperature range of NE5565 is 0~+85℃. The main features of NE5565 are: ●The same chip can complete PFC and ballast dimming control; ●AC current harmonic distortion is very low; ●Variable frequency mode; ●Programmable preheating and ignition to achieve three-step soft start; ● Lamp overvoltage protection; ●Can eliminate the overshoot generated when the load is cut off to achieve overvoltage protection. 2. Main functions of NE5565 The typical application circuit of NE5565 is shown in Figure 3. T1 is the high-frequency transformer of the half-bridge oscillator, and T2 is the lamp current detection transformer. 2.1 The 7.42V reference voltage output by the VREF pin of the voltage regulator (voltage regulator) is used as the reference for the control logic voltage. Vcc is usually 12.7V, and before VREF is output, Vcc is at least 9.3V. The accuracy of VREF is ±3.5% in the range of 0 to 85°C. 2.2 The lamp voltage regulator must limit the maximum open circuit voltage across the lamp load under conditions such as preheating, ignition and lamp shutdown. During the voltage stabilization operation, the lamp voltage is controlled by the arc voltage of the lamp and is not controlled by the control circuit. When the VLAMP pin voltage exceeds VREF, the lamp voltage comparator detects the VLAMP pin voltage. During this time, the lamp voltage reaches the maximum allowable open circuit voltage value, and the VLAMP voltage is reduced through the rapid frequency increase circuit. The RXCX time constant determines the frequency offset time of the startup circuit (ratio 2:1). 2.3 Low-voltage lockout protection When the PFC and half-bridge control circuit should be turned on or off, the protection circuit uses a Schmeiss trigger to detect the DC power supply voltage of the Vcc pin and determine the upper and lower limit trip points of the power supply voltage. When Vcc rises from zero volts to the upper limit voltage value (11V), the PFC and half-bridge control circuits remain off. Once Vcc exceeds the upper limit voltage, the PFC and half-bridge oscillator circuits start to work. When Vcc is lower than the lower limit voltage (10V), the PFC and half-bridge circuit are turned off. Before Vcc exceeds the upper limit trip point, the PFC and half-bridge oscillator are not allowed to operate. The minimum delay is set by components external to the DMAX pin. 2.4 Lamp starting and PFC overvoltage protection The half-bridge undervoltage lockout circuit samples the DC output voltage of the PFC. Before the PFC output voltage reaches the set value (such as 400VDC), the undervoltage blockade circuit prohibits the lamp from igniting. When the OV pin input voltage exceeds 5/7 VREF, the inverter frequency changes from the maximum value during lamp preheating to normal lamp ignition. The lower frequency offset at the time, and the ignition sequence is started. The overvoltage protection circuit prevents the PFC DC output voltage from exceeding the set value. When the overvoltage comparator input pin OV voltage is much higher than VREF, the PFC buffer gate drive output OUTP is turned off to prevent the PFC DC output voltage from further increasing. The overvoltage protection circuit only protects the overvoltage or overshoot generated by the PFC circuit and cannot suppress the transient voltage of the AC line. 2.5 Capacitive load protection The capacitive load protection circuit is used to prevent the failure of the half-bridge power transistor when the lamp is removed. At frequencies above the resonant frequency of the half-bridge LC load network, the primary voltage will lead the primary current. The protection logic detects the phase relationship between the LC network resonant current and voltage. The IPRIM pin input voltage is the primary current signal of the LC network. If the IPRIM pin voltage is higher than -100mV (positive), that is, when the gate drive signal is high level, the system will malfunction and the frequency of the half-bridge oscillator will increase. 2.6 Half-bridge oscillator The half-bridge oscillator is a triangle wave generator used to generate square wave signals to drive the buffer circuit. The oscillation frequency is determined by the resistance and capacitance values ​​of RT and CT pins, and the CT pin voltage is a triangular wave voltage. 2.7 Output buffer driver The output buffer is used as